According to statistical reports by China's elevator association, in China the number of elevators being used is now 1.5 million, and the number of sold elevators is increasing by more than 150 thousand per year. This means China has become an elevator superpower in the world. With increasing number of elevators used in China, an electricity consumption amount of a typical elevator is approximate 50-100 kWh/day. By electricity consumption per day of 80 kWh for each elevator, with the conservative estimated elevator numbers of 1.5 million, the total electricity consumption per day is calculated approximate 120 million KWh, and hence the total electricity consumption per year is 43.8 billion KWh. In this manner, the energy consumption per year of the whole China elevators is equivalent to seven-month energy generation by the Three Gorges' Hydropower Station. Evidently, the elevator energy consumption is tremendous. Therefore, this brings an elevator energy-conservation demand without a moment delay. Energy-conserving elevators are the inevitable trends in the future elevator development.
The elevator travel regulation is very special, primarily including ascending and descending movements each for 50%. When the elevator is in an ascending condition without load, the counter-weight of the elevator pulls the elevator so that a tractor of the elevator is in an energy generating state; similarly, when the elevator is in a descending condition with a full load, the elevator is also in an energy generating state.
The tractor of the elevator is in the energy generating state when ascending in a no-load condition and descending in a full-load condition so that DC voltage of a driver is raised by the energy generated by the tractor. In order to ensure the driver operating normally, the energy generated by the tractor needs to be released. A traditional method is to add a braking unit and a braking resistor to the driver, namely a heat dissipation approach, to dissipate the energy generated by the tractor by the braking resistor.
Because the energy generated by the tractor is dissipated by the braking resistor in heat dissipation, the energy is not effectively utilized. Currently there are a few methods involving effective utilization of the dissipated energy, and three methods are discussed in the following.
1. A method of adopting a large capacitor is introduced. When the tractor of the elevator is in the energy generating state, the large capacitor is charged through a circuit so that the energy in the large capacitor can be utilized for a control circuit of the driver. The method adopting the large capacitor is an advancement of reutilization of the energy generated by the tractor but electric power of the control circuit of the driver is low, and the energy consumption the control circuit of the driver is also low so that a part of the energy generated by the tractor that cannot be completely stored in the large capacitor is still necessarily dissipated by the braking resistor in heat dissipation.
2. A method of adopting storing-energy batteries is introduced, the principle of which is the same as the large capacitor method described above.
3. A simpler energy-conserving method is to power-off the driver and a lighting power when the elevator is in a standby state. In fact, this energy-conserving method cannot completely solve the problem of elevator energy consumption.
The above-mentioned methods cannot completely accomplish purposes of conserving energy.